add new API, but empty impl

include/core/SkImageGenerator.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkImageGenerator_DEFINED
 #define SkImageGenerator_DEFINED
 
@@ skipping 98 matching lines @@
      *  rowBytes are both fully defined and non NULL/non 0 or they are both NULL or have NULL or 0
      *  entries only. Having only partial planes/rowBytes information is not supported.
      *
      *  If all planes and rowBytes entries are non NULL or non 0, then it should copy the
      *  associated YUV data into those planes of memory supplied by the caller. It should validate
      *  that the sizes match what it expected. If the sizes do not match, it should return false.
      */
     bool getYUV8Planes(SkISize sizes[3], void* planes[3], size_t rowBytes[3],
                        SkYUVColorSpace* colorSpace);
 
+    /**
+     *  If the default image decoder system can interpret the specified (encoded) data, then
+     *  this returns a new ImageGenerator for it. Otherwise this returns NULL. Either way
+     *  the caller is still responsible for managing their ownership of the data.
+     */
+    static SkImageGenerator* NewFromData(SkData*);
+
 protected:
     virtual SkData* onRefEncodedData();
     virtual bool onGetInfo(SkImageInfo* info);
     virtual bool onGetPixels(const SkImageInfo& info,
                              void* pixels, size_t rowBytes,
                              SkPMColor ctable[], int* ctableCount);
     virtual bool onGetYUV8Planes(SkISize sizes[3], void* planes[3], size_t rowBytes[3]);
     virtual bool onGetYUV8Planes(SkISize sizes[3], void* planes[3], size_t rowBytes[3],
                                  SkYUVColorSpace* colorSpace);
 };
 
 #endif  // SkImageGenerator_DEFINED